Why is plasma membrane called semi-permeable membrane ? Write one function of it.

Plasma membrane is also known as semi permeable as it allows certain molecules to pass through it while stopping others.

Functions of cell membrane

• It protects intracellular organelles from the outside environment.
• It selectively allows the molecules to move in and out of the cell. Gases such as carbon dioxide and oxygen pass through diffusion, while other small molecules such as sugar pass through a process called passive transport. Ions such as sodium or potassium are transported through a process called active transport (with the utilization of ATP). Movement of water molecules through the membrane takes place by osmosis.
• It can also engulf or expel substances in and out of the cell through endocytosis or exocytosis respectively. Endocytosis is the process through which cells take in extra-cellular substances. Endocytosis represents both phagocytosis (ingestion of whole food),and pinocytosis (ingestion of water).
• It establishes communication between cells.